The present invention relates generally to implantable pacemakers and more particularly to subcutaneous electrodes implemented to sense, acquire, and store electrocardiographic data and waveform tracings from an implanted pacemaker. More particularly, the present invention relates to various embodiments including the manufacture and assembly of such electrodes with feedthroughs that facilitate their electrical connection to a pacemaker""s circuitry.
Electrocardiogram (ECG) signals are commonly used in medicine to determine the status of the electrical conduction system of the human heart. As practiced, an ECG recording device is commonly attached to the patient via ECG leads connected to skin electrodes arrayed on the patient""s body so as to achieve a recording that displays the cardiac waveforms in any one of 12 possible vectors.
Since the implantation of the first cardiac pacemaker, implantable IMD technology has advanced with the development of sophisticated, programmable cardiac pacemakers and pacemaker-cardioverter-defibrillator (PCD) arrhythmia control devices designed to detect arrhythmias and dispense appropriate therapies. The detection and discrimination between various arrhythmic episodes in order to trigger the delivery of an appropriate therapy is of considerable interest. Prescription for implantation and programming of the implanted device are based on the analysis of the PQRST electrocardiogram (ECG) and the electrogram (EGM). The waveforms are usually separated for such analysis into the P-wave and R-wave in systems that are designed to detect the depolarization of the atrium and ventricle respectively. Such systems employ detection of the occurrence of the P-wave and R-wave, analysis of the rate, regularity, and onset of variations in the rate of recurrence of the P-wave and R-wave, the morphology of the P-wave and R-wave and the direction of propagation of the depolarization represented by the P-wave and R-wave in the heart. The detection, analysis and storage of such EGM data within implanted medical devices are well known in the art. Acquisition and use of ECG tracing(s), on the other hand, has generally been limited to the use of an external ECG recording machine attached to the patient via surface electrodes of one sort or another.
The aforementioned ECG systems that use detection and analysis of the PQRST complex are all dependent upon the spatial orientation and number of externally applied electrodes available near or around the heart to detect or sense the cardiac depolarization wave front.
As the functional sophistication and complexity of implantable medical device systems increased over the years, it has become necessary for such systems to include communication means between implanted devices and/or an external device, for example, a programming console, monitoring system, and similar systems. For diagnostic purposes, it is desirable that the implanted device be able to communicate information regarding the device""s operational status and the patient""s condition to the physician or clinician. State of the art implantable devices are available which can transmit or telemeter a digitized electrical signal to display electrical cardiac activity (e.g., an ECG, EGM, or the like) for storage and/or analysis by an external device.
To diagnose and measure cardiac events, the cardiologist has several tools from which to choose. Such tools include twelve-lead electrocardiograms, exercise stress electrocardiograms, Holter monitoring, radioisotope imaging, coronary angiography, myocardial biopsy, and blood serum enzyme tests. In spite of these advances in the medical device art, the surface ECG has remained a standard diagnostic tool since the very beginning of pacing and remains so today. The twelve-lead electrocardiogram (ECG) is generally the first procedure used to determine cardiac status prior to implanting a pacing system. Thereafter, the physician will typically use an ECG available through the programmer or extra corporeal telemetry transmission to check the pacemaker""s efficacy after implantation. Previous ECG tracings are placed into the patient""s records for later use in comparing against more recent tracings. It must be noted, however, that current art practice in ECG recording (whether through a direct connection to an ECG recording device or to a pacemaker programmer), involves the use of external ECG electrodes and leads.
Unfortunately, surface ECG electrodes have technical drawbacks. For example, electrocardiogram analysis performed using existing external or body surface ECG systems can be limited by mechanical problems and poor signal quality. Electrodes attached externally to the body are a major source of signal quality problems and errors because of susceptibility to interference such as muscle noise, electromagnetic interference, high frequency communication equipment interference, and baseline shift from respiration, for example. Signal degradation also occurs due to contact problems, ECG waveform artifacts, and patient discomfort. Externally attached electrodes are also subject to motion artifacts from positional changes and the relative displacement between the skin and the electrodes. Furthermore, external electrodes require special skin preparation, for example, application of electrolyte ointment or cream, to ensure adequate electrical contact. Such preparation, along with positioning the electrode and attachment of the ECG lead to the electrode needlessly prolongs the pacemaker follow-up session. One possible approach is to equip the implanted pacemaker with features for detecting cardiac signals and transforming them into a tracing that is the same as or comparable to tracings obtainable via ECG leads attached to surface (skin) electrodes.
Monitoring electrical activity of the human heart for diagnostic and related medical purposes is well known in the art. For example, U.S. Pat. No. 4,023,565 issued to Ohlsson describes circuitry for recording ECG signals from multiple lead inputs. Similarly, U.S. Pat. No. 4,263,919 issued to Levin, U.S. Pat. No. 4,170,227 issued to Feldman, et al, and U.S. Pat. No. 4,593,702 issued to Kepski, et al, describe multiple electrode systems that combine surface EKG signals for artifact rejection.
The primary application of multiple electrode systems in the prior art appears to be vector cardiography from ECG signals taken from multiple chest and limb electrodes. This is a technique for monitoring the direction of depolarization of the heart including the amplitude of the cardiac depolarization waves. U.S. Pat. No. 4,121,576 issued to Greensite discloses such a system.
Numerous body surface ECG monitoring electrode systems have been implemented in the past to detect the ECG and conduct vector cardiographic studies. For example, U.S. Pat. No. 4,082,086 issued to Page, et al., discloses a four electrode orthogonal array that may be applied to the patient""s skin both for convenience and to ensure precise orientation of one electrode with respect to the other. U.S. Pat. No. 3,983,867 issued to Case describes a vector cardiography system employing ECG electrodes disposed on the patient in commonly used locations and a hex axial reference system orthogonal display for displaying ECG signals of voltage versus time generated across sampled bipolar electrode pairs.
U.S. Pat. No. 4,310,000 to Lindemans and U.S. Pat. Nos. 4,729,376 and 4,674,508 to DeCote, incorporated herein by reference, disclose the use of a separate passive sensing reference electrode mounted on the pacemaker connector block or otherwise insulated from the pacemaker case. The passive electrode is implemented to provide a sensing reference electrode that is not part of the stimulation reference electrode and thus does not carry residual after-potentials at its surface following delivery of a stimulation pulse.
Moreover, in regard to subcutaneously implanted EGM electrodes, the aforementioned Lindemans U.S. Pat. No. 4,310,000 discloses one or more reference sensing electrodes positioned on the surface of the pacemaker case as described above. In a related art, U.S. Pat. No. 4,313,443 issued to Lund describes a subcutaneously implanted electrode or electrodes for use in monitoring ECG.
U.S. Pat. No. 5,331,966 to Bennett, incorporated herein by reference, discloses a method and apparatus for providing an enhanced capability of detecting and gathering electrical cardiac signals via an array of relatively closely spaced subcutaneous electrodes (located on the body of an implanted device).
More recently, P-9033 Surround Shroud Connector and Electrode Housings for a Subcutaneous Electrode Array and Leadless ECGs, by Ceballos, et al. filed on Oct. 26, 2000, Ser. No. 09/697,438, incorporated herein by reference in its totality, discloses an alternate method and apparatus for detecting electrical cardiac signals via an array of subcutaneous electrodes located on a shroud circumferentially placed on the perimeter of an implanted pacemaker. An associated submission, P-9041 Subcutaneous Electrode for Sensing Electrical Signals of the Heart by Brabec et al, filed on Oct. 31, 2000, Ser. No. 09/703,152, incorporated herein by reference in its totality, discloses the use of a spiral electrode implemented in conjunction with the shroud described in P-9033. In addition, P-8786 Multilayer Ceramic Electrodes for Sensing Cardiac Depolarization Signals, filed Oct. 25, 2000, Ser. No. 09/696,365 and P-8787 Thin Film Electrodes for Sensing Cardiac Depolarization Signals, filed on Dec. 13, 2000, Ser. No. 09/736,046 both by Guck et al, incorporated herein by reference in their totality, disclose the use of multi-layer ceramic and thin film ECG electrodes placed into recesses incorporated along and into the peripheral edge of the implantable pacemaker.
The present invention relates to various electrode designs that allow direct incorporation of the electrode into a feedthrough. Depending on the design, the feedthrough ferrules may be welded individually into desired positions around the perimeter of an implantable pacemaker and then the feedthrough/electrodes fabricated into the existing ferrules. Alternatively, the complete feedthrough/electrode assembly may be fabricated and then welded as one body into the pacemaker. These feedthrough/electrode assemblies are electrically connected to the circuitry of an implantable pacemaker to create a leadless Subcutaneous Electrode Array (SEA) for the purpose of detecting cardiac depolarization waveforms displayable as electrocardiographic tracings on an external device in communication with the pacemaker. When the programming head of a programmer is positioned above an implanted device equipped with a leadless SEA electrocardiographic tracing waveforms may be displayed and viewed on the programmer screen. These waveforms may also be telemetered extra-corporeally to an external device located nearby or at some distance from the patient, as is described in P-7683, Leadless Fully Automatic Pacemaker Follow-Up by Combs and Berg, filed on Dec. 27, 2000, Ser. No. 09/749,169 incorporated herein by reference in its entirety.
The present invention, inter alia, may be a replacement for externally mounted electrodes and electrode wires in the prior art currently used on the leadless ECG implantable pacemaker, as described in U.S. Pat. No. 5,331,966 issued to Bennett. Typically, prior art practice includes electrodes placed on the face of the implanted pacemaker. When facing muscle, the electrodes are apt to detect myopotentials and are susceptible to baseline drift. The present invention minimizes myopotential detection and thereby makes the pacemaker less sensitive to orientation in the incision pocket of a patient. Further, allowing the device to be implanted on either side of the chest provides maximum electrode separation and minimal signal variation. This is primarily because of variations in pacemaker orientations within the pocket. Implantable device electrodes need to be placed on the perimeter of the pacemaker in such a way as to maximize the distance between electrode pairs.
The present invention eliminates the need for a compliant shroud that typically houses the surface mounted electrodes and connecting wires as described in patent application No. P-9033, xe2x80x9cSurround Shroud Connector And Electrode Housings For A Subcutaneous Electrode Array And Leadless ECGs,xe2x80x9d by Ceballos et al. filed on Oct. 26, 2000, Ser. No. 09/697,438. Because the feedthrough/electrode assembly is an integral functional component, the complete assembly can be welded directly into the IPG casing. The present invention, including the manufacturing process disclosed herein eliminate the need for a compliant shroud in addition to structural efficiencies and ease of handling of the implantable pacemaker during the implant procedure.
The spacing of the electrodes in the present invention provides maximal electrode spacing, minimal myopotential electrical noise, and, at the same time, appropriate insulation from the pacemaker casing particularly because of the welding of the assemblies to the pacemaker casing. The electrode spacing around the pacemaker""s perimeter preferably maintains a maximum and equal distance between the electrode pairs. Spacing arrangements such as disclosed with the three-electrode equal spacing embodiment maintain a maximum average signal. The arrangement is preferred because the spacing of the three vectors between the electrode pairs is equal and the angle between the vectors is equilateral, as is shown using mathematical modeling. Such an arrangement of electrode pairs also minimizes signal variation. An alternate three-electrode embodiment includes electrodes arranged so that the spacing of two vectors is equal and with angle between them set at 90xc2x0. Vectors in these embodiments can be combined to provide adequate sensing of cardiac signals (ECGs). Further disclosure of the position of three and four-electrodes in the Subcutaneous Electrode Array (SEA) may be found in P-8552, Subcutaneous Electrode Array Virtual ECG Lead by Panken and Reinke, filed on Nov. 22, 2000, Ser. No. 09/721,275, incorporated herein by reference in its entirety.
Similar to the use of a compliant shroud, helical electrode and multi-layer ceramic electrode, the present invention allows a physician or medical technician to perform leadless follow-up that, in turn, eliminates the time it takes to attach external leads to the patient. Such timesavings may significantly reduce the cost of follow-up, and may enable the physician or medical technician to see more patients. Other implementations include, but are not limited to: Holter monitoring with event storage, arrhythmia detection and monitoring, capture detection, ischemia detection and monitoring (S-T elevation and suppression on the ECG), changes in QT interval, and transtelephonic and telemetric monitoring.